3 Answers
3

The Ubuntu installer will give you the option to resize your partitions, there will be a optionto install it next to windows, use up the whole disk, and 1 that says 'something else' in which you can manually set all the partitions you'd like, like that common data one.

2) Shrink your C or D drive. - This can be done in Windows quite easily, you can use GpartEd if you really want to but it is not necessary. There are thousands of guides how to do this with either option so I'm not going to go into too much detail.

3)Format the Data partition to FAT32 or get NTFS support for Ubuntu - Formatting the shared drive to FAT32 will be the easier option as it is supported off the bat by both distros, but I believe it gives you a file size limit of about 4gb. If you choose to go the NTFS route, there are plenty of guides available to guide you through that process.

Whatever you have described seems like a lot of work to do. I would prefer formatting the hard drive and starting everything afresh. This seems like less haste. However, follow the steps below to get what you want. Remember to create a backup of all your data before starting.

Install whichever partition tool that you prefer.

Re size one of your partitions and allocate some space for the Ubuntu partition.
Format it to ext4. Ubuntu runs on ext4. Ubuntu doesn't require much space, so whatever is left is for your "big" common partition. You can access the files on Ubuntu from windows using "ext2explore". You can directly access all files in your hdd from ubuntu without using any additional software.

Download the Ubuntu ISO from the Ubuntu website. 14.04 is the LTS version, or you can get the latest 14.10 if you want to. Write the Ubuntu ISO to a DVD and boot from that.

Installation is pretty simple and there are a lot of guides out there to do that. Moving on.

Now that you have successfully installed Ubuntu, you got to set the MBR right. Use syslinux to get the job done, if GRUB hadn't already been installed and you have trouble booting into the system.